Various techniques are known for protecting computer readable media, such as optical discs including CDs and DVDs, against unauthorised copying. Two such methods of protection are described in our earlier U.S. Ser. No. 10/848,879 and U.S. Ser. No. 10/939,186, both of which are incorporated herein by reference.
U.S. Ser. No. 10/848,879 discloses a method of protection in which redundant control data, including errors, is included amongst the data carried by an optical disc. The control data controls access to content files on the optical disc, containing material or content data to be played, and the redundant control data is not utilized during normal playback of the content. However, during unauthorized copying, the redundant control data is accessed and the errors in such data are arranged to frustrate navigation of at least one program path providing access to the content data.
U.S. Ser. No. 10/939,186 discloses a method of protection in which at least one region containing unreadable or subversive data is provided within the content data on an optical disc. Control data on the disc for accessing content files containing the content data ensures that access to the region of unreadable or subversive data is prevented during normal playback. However, in the event of unauthorised copying, the region of unreadable or subversive data is accessed and hinders or prevents copying.
The methods according to these two earlier U.S. patent applications are both passive, in the sense that they rely on data incorporated in the optical disc for protecting the disc against a procedure known as “ripping”, i.e. unauthorised copying onto a hard drive of a local computer or network.
Such passive techniques are effective to some extent in protecting against unauthorised copying. However, ripping software is becoming increasingly sophisticated and powerful and increasingly effective in overcoming such passive forms of protection.
There is, therefore, a need for more effective forms of protection against unauthorised copying and for forms of protection that are harder to circumvent.